An automated battery test system with four major functions 1) battery environmental control, 2) battery discharge-recharge cycling, 3) data collection and recording, and 4) failure warning and diagnosis, has been designed and built. Accelerated testing of rechargeable pacemaker batteries with this test rack has consistently demonstrated from 16 to 20 years function under biological conditions. In addition, real time studies continue on 5 to 6 year old functional rechargeable batteries from the original epoxy potted pacemakers built with this study. Six low-drain, hermetically sealed, fixed rate pacemakers have been implanted during the last year and the mean drain during function with the high current density, ball-tip lead approximates 25 microamps. This necessitates 3 minutes recharging daily or approximately 6 hours charging every 6 months to keep the units fully charged. No circuitry battery or case problems have been encountered with these units and studies will be continued during the coming project year. In addition, 6 low-drain, hermetically sealed, demand pacemakers are nearing completion and implantation and chronic testing in these units will begin shortly.